1. Field of the Invention
This invention relates to an assembly for cutting samples from a center-perforated solid propellant grain for testing and evaluation purposes, and to a method of cutting the solid propellant grain with the assembly.
2. Description of the Related Art
Solid propellant rocket motors contain a solid propellant comprised of various ingredients, including binders, for example, curing agents and catalysts, fuels, oxidizers, and fillers. The presence of each of these ingredients in acceptable concentrations and consistencies is essential for ensuring proper and predictable motor operation upon ignition of the solid propellant.
Therefore, substantial amounts of testing are performed on solid propellant grains. These tests usually involve removing a sample from the propellant grain after it is cast and cured. Removal of the propellant grain sample has conventionally involved the use of manual cutting tools, such as knives and saws. However, a drawback of manual cutting of the propellant grain is production of inconsistent shaped samples with insufficiently smooth surfaces to permit satisfactory analysis and testing. Another drawback of these manual techniques is that the manual cutting of the propellant grain places the operator at great risk from, for instance, an accidental ignition of the propellant.
It is therefore an object of this invention to provide a propellant cutting assembly and process that significantly improves the repeatability and consistency of the cut sample while reducing the risk from accidental ignition.
In accordance with the principles of this invention, this and other objects are attained by the provision of a solid propellant cutting assembly suitable for making radial cuts into an annular solid propellant grain having a central bore of a predetermined diameter. In accordance with an embodiment of this invention, the assembly comprises one or more extension beams extending in length between a proximal end and a distal end thereof. The length of the extension beams is less than the diameter of the central bore so as to permit the assembly to be loaded into the central bore. Proximal and distal retaining heads are respectively provided at proximal and distal ends of the extension beams. Preferably, the retaining heads have respective curvilinear surfaces that are complementary to an inner surface of the central bore and face away from the extension beams. An adjustment mechanism interposed between the extension beams and either the distal retaining head or the proximal retaining head permits relative movement of the distal and proximal retaining heads away from and towards each other. When the retaining heads are moved towards each other into a loading position, the distance between the curvilinear surfaces of the distal and proximal retaining heads is less than the diameter of the central bore. As a consequence, the assembly may be loaded into the central bore and positioned so that the extension beams are oriented as desired. The adjustment mechanism can then be actuated to increase the distance between the proximal and distal retaining heads so that the distance between the curvilinear surfaces of the distal and proximal retaining heads is substantially equal, but slightly smaller than, the diameter of the central bore. As a consequence, the curvilinear surfaces of the heads contact diametrically opposed positions of the inner surface of the propellant grain and wedge the assembly into position. A cutting blade assembly is provided at the proximal end of the extension beams. A driving mechanism is provided to drive the cutting blade past the ends of the extension beams and into the solid propellant. A level is also provided to orient the blade appropriately for achieving a cut of uniform thickness.
This invention is also directed to a process of making radial cuts in a propellant grain with the above-discussed assembly for the purpose of removing samples for testing and analysis.
This invention may be used for sampling various types of central-perforatedpropellant grains and hybrid fuel grains.